Newly developed paramagnetic probes (by NTCO, Sweden) were characterized in X-band and L-band both in vitro and in vivo. The response of the paramagnetic probes to oxygen concentration were calibrated in X-band at 37xC. The distribution and decay of these compounds in various organs (liver, brain, lung, bladder, muscle, etc.) were measured in live mice and isolated organ respectively in L-band. Properties in vitro of these probes were investigated with cell culture in X-band.